It is common practice to irrigate crop areas in those regions where there is a shortage of rainfall. One method of irrigation is by furrow irrigation. A problem with furrow irrigation is that the irrigation water flowing along the furrow is liable to erode the furrow. Also infiltration of the water through the furrow may not be as efficient as is desired. It is known to include synthetic polymer in the furrow irrigation water, the polymer often being the type which is commercially available for improving the structure of soil by direct application of the polymer to the soil. Furrow irrigation processes using such polymers are described particularly in WO96/102126.
Another way of irrigating crop areas is by spraying water onto the area. Because there is no deliberate flow of water along the surface, it might be thought that erosion would not be a problem. However erosion problems can occurs especially when the irrigated area is on a slope. Also infiltration may not be as efficient as is desirable, especially when the irrigated soil is allowed to dry out between irrigations, for instance as is likely to occur in large pivot irrigation systems where there may be a day or more between irrigations. Also not all the spray water is effective for irrigation, for instance due to run-off or evaporation.
It would be desirable to be able to minimise these deficiencies in large-scale spray irrigation.
It might be thought that introduction of polymers, for instance of the type known as soil conditioners, into the irrigation water would be beneficial. Unfortunately existing methods are not practicable.
Polymers are generally supplied initially as a powder or as a reverse phase emulsion (i.e., a dispersion of polymer particles in a non-aqueous liquid, generally oil). The normal industrial practice is to mix the powder or the reverse phase emulsion with water in special dissolution apparatus so as to form an aqueous solution of the polymer having a concentration of, for instance, 0.2 to 2% by weight and this solution is then dosed into the water which is to be treated by the polymer.
However the manufacture of this solution necessitates the provision of special make-up apparatus. It is impracticable to provide this make-up apparatus at the crop area, and if the solution is made up at a point distant from the crop area it is then necessary to transport the solution to the crop area and this is inconvenient because of the large volume of the solution.